1. Field of the Invention
This invention relates to apparatus for driving a winding reel to take up a web material from an unwinding reel, and more particularly to a mechanism for controlling the driving torque force applied to the web transport mechanism in accordance with the quantity of web material taken up on the winding reel.
2. Description of the Prior Art
It is generally known that as a web material is pulled from an unwinding reel and is taken up on a winding reel, the driving torque necessary for the winding reel to take up the web material is gradually decreased with the increasing diameters of the core of web material on the winding reel as it winds in, the difference between driving torques in initial and final stages of the entire reeling operation being made larger with a longer length of the web material with a larger winding diameter of the entire web material wound on either reel.
With a film cassette, for example, in a cine camera, therefore, it is necessary to compensate for the difference in the driving torque so as to maintain constant the stress on the film strip between the reels during entire cassette operation, or otherwise, in an initial state of the reeling operation where the film transport mechanism is subject to a larger load, the unwinding reel is driven to rotate at a slower rate, while in a final state where the film transport mechanism is subject to a smaller load, it is driven to rotate at a faster rate, it being recognized that this kind of action not only seriously affects the quality of reproduction in image recordings, but sometimes gives rise to failure in image recordings.
Also in the case of player-recorders, similar problems to those described above are encountered, if not resolved by providing some means for controlling the driving torque in accordance with the varying winding diameters of the tape web on the winding reel, resulting not only in an unstability of sound records and reproductions, but also in sound discontinuity.
In order to accomplish the desired driving control of the reels, conventional motion picture cameras of large size adapted for use with 70 mm, 35 mm and 16 mm frame size film reels, and open reel type tape recorders of large size adapted for use with large-diameter reels have utilized a system for controlling the driving torque as the quantity of tape or film wound on the take up reel is varied. Such system results in an expensive, complex and bulky mechanism which is undesirable for use in cine cameras of compact type, for example, of 8 mm frame size as well as in tape recorders of compact type.
On the other hand, the system for travelling magnetic sound tape or film strip between a pair of reels which are enclosed in a cassette has found a wide acceptance in the fields of cine cameras of 8 mm frame size and tape recorders of compact type. Particularly, in the reel-to-reel system wherein one of the coplanar reels to which the respective ends of a tape web are attached is driven to take up the tape web from the other reel, the above-mentioned problems which make reliable cassette operation difficult to achieve remains unsolved. As a result, differential pulls arise with corresponding differences in rate of rotation of the reels owing to constantly changing diameters of the core of tape web on each reel as one unwinds and the other winds in, it not scarcely happening that such an action gives rise to breakage and damaging stresses on the tape web.